Electrical connection are widely used in components such as printed electrical circuits, electronic conductors and contacts or other electrical devices for delivering data signals. The electrical connection between components is typically achieved using techniques such as flexible wires with connectors attached to the ends thereof or flexible printed circuits equipped with special connectors such as copper bumps to electrically couple with other external devices. Specifically, disk drive unit also employs electrical connection structures to achieve information storing or reproducing function.
In related art, referring to FIG. 1, a typical disk drive unit comprises a head stack assembly with sliders thereon, a printed circuit board assembly for controlling the operation of the head stack assembly, a stack of disks 110 for suspending respective sliders and a spindle motor 120 for spinning the disks 110. A voice coil motor (VCM) 140 is connected to the head stack assembly for controlling the motion of the head stack assembly and, in turn, controlling the respective sliders to position with reference to data tracks across the surface of the corresponding disks.
Common head stack assembly comprises a plurality of head gimbal assemblies. Such head gimbal assemblies possess the same structures and configurations. As for illustration, also referring to FIG. 1, a head gimbal assembly 150 with a slider 151 is connected to a drive arm 130 which is controlled by the voice coil motor 140. As is shown in FIG. 2, the head gimbal assembly 150 includes a suspension 152 having a base plate 153, a load beam 156, a hinge 154 and a flexure 155. The load beam 156 is connected to the base plate 153 by the hinge 154. The flexure 155 is made of flexible material and runs from the hinge 154 to the load beam 156. One end of the load beam 156 is mounted to the drive arm 130 (referring to FIG. 1) by means of the base plate 153, and the other end of the load beam 156 is attached to the flexure 155. The load beam 156 biases the slider 151 toward the surface of the disk 110, while the flexure 155 provides flexibility for the slider 151.
The slider 151 is electrically coupled with a printed circuit board assembly (PCBA) of the control system via a wire member or flexible printed circuit 165. Specifically, the flexure 155 forms a plurality of bonding pads 158 thereon and the flexible printed circuit 165 provides copper bumps 168 corresponding to the respective bonding pads 158 of the flexure 155. The slider 151 is electrically connected with one end of the bonding pad 158 of the flexure 155 via a plurality of traces 157. The other end of the bonding pad 158 is solder-bonded with the corresponding copper bump 168 of the flexible printed circuit 165. As the bonding pad 158 of the flexure 155 is established electrical connection with the flexible printed circuit 165, the slider 151 can selectively read from or write to the disk 110 (referring to FIG. 1) according to the signal conducting from printed circuit board assembly under the control system.
Referring to FIG. 3, as in the prior art, each bonding pad 158 of the flexure 155 (shown in FIG. 2) possesses a layered structure. That is, each bonding pad 158 is formed by sequentially depositing a Cu film 158a, an Ni film 158b and an Au film on a base film 158c of the flexure. The Ni film 158b can prevent oxidation of the Cu film 158a and the Au film on the surface of the Ni film 158b can improve the wettability of the bonding pad 158. Each copper bump 168 of the flexible printed circuit 165 is covered by a solder layer around the whole surface thereof.
When soldering, each copper bump 168 of the flexible printed circuit 165 is aligned with and pressed to the corresponding bonding pad 158 of the flexure 155 with sufficient force to keep a correct alignment and ensure an intimate contact therebetween. Then heat the flexible printed circuit 165 and the flexible 155 which are placed to be sandwiched between a heater and a holding plate for heating beforehand. Thus the solder layer of the copper bump 168 is melted and a solder junction portion 100′ bonding the bonding pad 158 of the flexure 155 and the copper bump 168 of the flexible printed circuit 165 is thus formed.
In the prior method, pressure and heat play a vital roll in the electrical connection quality in the solder-bonding. If both the pressure and the heat imposed to the copper bumps 168 and the bonding pads 158 are just sufficient, two adjacent copper bumps 168a, 168b of the flexible printed circuit 165 (shown in FIG. 2) could be respectively well solder-bonded with corresponding adjacent bonding pads of the flexure. Accordingly, a space could exist between the two copper bumps, which ensures a sound electrical circuit and further enables a good read/write performance of the slider. However, if either of the pressure and the heat is excessive when doing solder-bonding, referring to FIG. 4, the solder layer of copper bumps 168a, 168b would boil, thus solder material covered the respective copper bumps 168a, 168b may spread out. Because of space limitation, the corresponding bonding pads 158, 158′ may locate very close and thus the spread solder material may cause the copper bump 168a to short with the adjacent bump 168b. Therefore, the electrical function of the head gimbal assembly 150 is greatly and seriously affected. Moreover, the solder-bonding needs pressure to ensure a high-quality electrical connection, but the pressure might damage the surrounding components of both the flexure 155 and the flexible printed circuit 165.
In addition, the prior solder-bonding is operated between opposite surfaces of the flexible printed circuit 165 and the flexure 155, therefore the operation is really difficult to control the spread solders which might induce occurrence of short-circuit and adversely affects the realization of electrical connection function. In all, the prior solder-bonding increases the complexity and difficulty of manufacturing process, and thus the manufacture yield is unsatisfactorily low and the cost is inappropriately high.
Hence, a need has arisen for providing a novel bonded structure of electrical components and a bonding method thereof, and a head gimbal assembly and a head stack assembly and a disk drive unit to solve the above-mentioned problems and achieve a good performance.